// SPDX-License-Identifier: GPL-2.0
/*
 *  linux/mm/swap_state.c
 *
 *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
 *  Swap reorganised 29.12.95, Stephen Tweedie
 *
 *  Rewritten to use page cache, (C) 1998 Stephen Tweedie
 */

/*
 * Official Linux v6.0: mm/swap_state.c
 * https://github.com/torvalds/linux/blob/v6.0/mm/swap_state.c#L174
 * Exact definition/declaration; not a reconstruction of a book listing.
 * See GPL-2.0.txt. Not a standalone translation unit.
 */

bool add_to_swap(struct folio *folio)
{
	swp_entry_t entry;
	int err;

	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
	VM_BUG_ON_FOLIO(!folio_test_uptodate(folio), folio);

	entry = folio_alloc_swap(folio);
	if (!entry.val)
		return false;

	/*
	 * XArray node allocations from PF_MEMALLOC contexts could
	 * completely exhaust the page allocator. __GFP_NOMEMALLOC
	 * stops emergency reserves from being allocated.
	 *
	 * TODO: this could cause a theoretical memory reclaim
	 * deadlock in the swap out path.
	 */
	/*
	 * Add it to the swap cache.
	 */
	err = add_to_swap_cache(&folio->page, entry,
			__GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN, NULL);
	if (err)
		/*
		 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
		 * clear SWAP_HAS_CACHE flag.
		 */
		goto fail;
	/*
	 * Normally the folio will be dirtied in unmap because its
	 * pte should be dirty. A special case is MADV_FREE page. The
	 * page's pte could have dirty bit cleared but the folio's
	 * SwapBacked flag is still set because clearing the dirty bit
	 * and SwapBacked flag has no lock protected. For such folio,
	 * unmap will not set dirty bit for it, so folio reclaim will
	 * not write the folio out. This can cause data corruption when
	 * the folio is swapped in later. Always setting the dirty flag
	 * for the folio solves the problem.
	 */
	folio_mark_dirty(folio);

	return true;

fail:
	put_swap_page(&folio->page, entry);
	return false;
}